Welcome to practical physicsPracticle physics - practical activities designed for use in the classroom with 11 to 19 year olds

Diffusion of copper sulfate solution in water


It is fascinating showing how liquids of different densities can be floated on top of each other before diffusion causes mixing at the interfaces.

Apparatus and materials

Gas jar

CuSO4 solution, concentrated (harmful)

Distilled water

Funnel and glass tube

Health & Safety and Technical notes

Concentrated copper sulfate solution (use 100 g in 250 ml of distilled water) is harmful. Wear eye protection while handling it.

Gas jars method 1 Gas jar showing start of mixing owing to diffusion

Photos courtesy of Mike Vetterlein  

You will need clear water on top of the copper sulfate solution. There are two ways of achieving this. Either put the water in first and then, carefully so as not to disturb the water, pour the denser copper sulfate solution into a funnel in a long tube so the solution goes under the water. Or, put the copper sulfate in first and, using a piece of bent glass tubing as shown, carefully add the water, keeping its outlet just below the water surface as its level rises.



a Show the newly-filled gas jar. 

b Leave undisturbed. 
c Get the class to check the gas jar each day.

Teaching notes

An optional variant is to put a strong sugar solution in the lower third of the jar, then add the concentrated copper sulfate solution, and finally the distilled water. Students will then see the copper sulfate diffusing against gravity as well as with it. 

This experiment was safety-checked in March 2005